Note: Descriptions are shown in the official language in which they were submitted.
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Description
Aluminum Conductor Composite Core Reinforced Cable and
Method of Manufacture
Technical Field
[1] The present invention relates to an aluminum conductor composite core
(ACCC)
reinforced cable and method of manufacture. More particularly, the present
invention
relates to a cable for providing electrical power having a composite core,
formed by
fiber reinforcements and a matrix, surrounded by aluminum conductor wires
capable
of carrying increased ampacity and operating at elevated temperatures.
Background Art
[2] Attempts have been made to develop a composite core comprised of a single
type
of fiber and thermoplastic resin. The object was to provide an electrical
transmission
cable which utilizes a reinforced plastic composite core as a load bearing
element in
the cable and to provide a method of carrying electrical current through an
electrical
transmission cable which utilizes an inner reinforced plastic core. The single
fiber /
thermoplastic composite core failed in these objectives. A one fiber /
thermoplastic
system does not have the required physical characteristics to effectively
transfer load
while keeping the cable from sagging. Secondly, a composite core comprising
glass
fiber and thermoplastic resin does not meet the operating temperatures
required for
increased ampacity, namely, between 90 C and 240 C, or higher.
[3] Physical properties of thermoplastic composite cores are further limited
by
processing methods. Previous processing methods cannot achieve a high fiber to
resin
ratio by volume or weight. These processes do not allow for creation of a
fiber rich
core that will achieve the strength required for electrical cables. Moreover,
the
processing speed of previous processing methods is limited by inherent
characteristics
of the process itself. For example, traditional extrusion / pultrusion dies
are ap-
proximately 36 inches long, having a constant cross section. The longer dies
create
increased friction between the composite and the die slowing processing time.
The
processing times in such systems for thermoplastic / thermoset resins range
from about
3 inches/minute to about 12 inches/minute. Processing speeds using polyester
and
vinyl ester resins can produce composites at up to 72 inches/minute. With
thousands of
miles of cables needed, these slow processing speeds fail to meet the need in
a fi-
nancially acceptable manner.
[4] It is therefore desirable to design an economically feasible cable that
facilitates
increased ampacity without corresponding cable sag. It is further desirable to
process
composite cores using a process that allows configuration and tuning of the
composite
cores during processing and allows for processing at speeds up to or above 60
ft/min.
Disclosure of Invention
Technical Problem
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[5] In a traditional aluminum conductor steel reinforced cable (ACSR), the
aluminum
conductor transmits the power and the steel core provides the strength member.
Conductor cables are constrained by the inherent physical characteristics of
the
components; these components limit ampacity. Ampacity is a measure of the
ability to
send power through the cable. Increased current or power on the cable causes a
cor-
responding increase in the conductor's operating temperature. Excessive heat
will
cause the conventional cable to sag below permissible levels, as the
relatively high co-
efficient of thermal expansion of the structural core causes the structural
member to
expand, resulting in cable sag. Typical ACSR cables can be operated at
temperatures
up to 75 C on a continuous basis without any significant change in the
conductor's
physical properties related to sag. Operated above 100 C, for any significant
length of
time, ACSR cables suffer from a plastic-like and permanent elongation, as well
as a
significant reduction in strength. These physical changes create excessive
line sage.
Such line sag has been identified as one of the primary causes of the power
blackout in
the Northeastern United States in 2003. The temperature limits constrain the
electrical
load rating of a typical 230-kV line, strung with 795 kcmil ACSR'Drake'
conductor, to
about 400 MVA, corresponding to a current of 1000 A. Therefore, to increase
the load
carrying capacity of transmission cables, the cable itself must be designed
using
components having inherent properties that allow for increased ampacity
without
inducing excessive line sag.
[6] Although ampacity gains can be obtained by increasing the conductor area
that
surrounds the steel core of the transmission cable, increasing conductor
volume
increases the weight of the cable and contributes to sag. Moreover, the
increased
weight requires the cable to use increased tension in the cable support
infrastructure.
Such large weight increases typically would require structural reinforcement
or re-
placement of the electrical transmission towers and utility poles. Such
infrastructure
modifications are typically not financially feasible. Thus, there is financial
motivation
to increase the load capacity on electrical transmission cables while using
the existing
transmission structures and liens.
Technical Solution
[7] An aluminum conductor composite core (ACCC) reinforced cable can
ameliorate
the problems in the prior art. The ACCC cable is an electrical cable with a
composite
core comprised of one or more fiber type reinforcements embedded in a matrix.
The
composite core is wrapped with electrical conductor wires. An ACCC reinforced
cable
is a high-temperature, low-sag conductor, which can be operated at
temperatures above
100 C while exhibiting stable tensile strength and creep elongation
properties. In
exemplary embodiments, the ACCC cable can operate at temperatures above 100 C
and in some embodiments, above 240 C. An ACCC cable with a similar outside
diameter may increase the line rating over a prior art cable by at least 50%
without any
significant changes in the overall weight of the conductor.
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[8] In accordance with the invention, in one embodiment, an ACCC cable
comprises a
core comprised of composite material surrounded by a protective coating. The
composite material is comprised of a plurality of fibers selected from one or
more fiber
types and embedded in a matrix. The important characteristics of the ACCC
cable are
a relatively high modulus of elasticity and a relatively low coefficient of
thermal
expansion of the structural core. The ACCC core, which is also smaller in
diameter,
lighter in weight, and stronger than previous core designs, allows an increase
the
ampacity of the conductor cable, by allowing the addition of additional
conductor
material in the same overall area, with an approximately equal weight. It is
further
desirable to design composite cores having long term durability. The composite
strength member should operate at a minimum of 40 years, and more preferably
twice
that, at elevated operating temperatures and in the other environmental
conditions to
which it will be exposed.
[9] In one embodiment, the invention discloses a composite core for an
electrical cable
comprising an inner core consisting of advanced composite material comprising
at
least one longitudinally oriented and substantially continuous reinforced
fiber type in a
thermosetting resin; an outer core consisting of low modulus composite
material
comprising at least one longitudinally oriented and substantially continuous
reinforced
fiber type in a thermosetting resin; and an outer film surrounding the
composite core,
wherein the composite core comprises a tensile strength of at least 160 Ksi.
[10] In a further embodiment, a method is disclosed for processing a composite
core for
an electrical cable. The steps comprise pulling one or more types of
longitudinally
oriented and substantially continuous fiber types through a resin to form a
fiber resin
matrix; removing excess resin from the fiber resin matrix; processing the
fiber resin
matrix through at least one first die type to compress the fibers into a
geometric shape
determined by the at least one die; introducing an outer film; wrapping the
outer film
around the composite core; processing the fiber resin matrix through at least
one
second die type to compress the composite core and coating; and curing the
composite
core and coating.
[11] In various embodiments, the protective coating aids in pultrusion of the
core during
manufacturing and functions to protect the core from various factors including
for
example, environmental conditions and effects on the resin comprising the
core.
Description of Drawings
[12] These and other features of the invention are best understood by
referring to the
detailed description of the invention, read in light of the accompanying
drawings, in
which:
[13] FIG.1 is a schematic view of one embodiment of an aluminum conductor
composite core (ACCC) reinforced cable showing an inner composite core and an
outer composite core surrounded by two layers of aluminum conductor according
to
the invention.
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[14] FIG. 1B is a schematic view of one embodiment of an aluminum conductor
composite core (ACCC) reinforced cable showing an inner composite core and an
outer composite core surrounded by an outer protective layer and two layers of
aluminum conductor according to the invention.
[15] FIG. 2 shows a cross-sectional view of five possible composite core cross-
section
geometries according to the invention.
[16] FIG. 3 shows a cross-sectional view of one embodiment of the method for
processing a composite core according to the invention.
[17] To clarify, each drawing includes reference numerals. These reference
numerals
follow a common nomenclature. The reference numeral will have three digits.
The first
digit represents the drawing number where the reference numeral was first
used.. For
example, a reference numeral used first in drawing one will have a numeral
like 1XX,
while a numeral first used in drawing four will have a numeral like 4XX. The
second
two numbers represent a specific item within a drawing. One item in FIG. 1 may
be
101 while another item may be 102. Like reference numerals used in later
drawing
represent the same item. For example, reference numeral 102 in FIG. 3 is the
same
item as shown in FIG. 1. In addition, the drawings are not necessarily drawn
to scale
but are configured to clearly illustrate the invention.
Best Mode
[18]
[19] An example of an ACCC reinforced cable in accordance with the present
invention
follows. An ACCC reinforced cable comprising four layers of components
consisting
of an inner carbon/epoxy layer, a next glass-fiber/epoxy layer, a Kapton
surface
material, and two or more layers of tetrahedral shaped aluminum strands. The
strength
member consists of an advanced composite T700S carbon/epoxy having a diameter
of
about 0.28 inches, surrounded by an outer layer of 250 yield Advantex E-
glass-fiber/epoxy having a layer diameter of about 0.375 inches. The glass-
fiber/epoxy
layer is surrounded by an inner layer of nine trapezoidal shaped aluminum
strands
having a diameter of about 0.7415 inches and an outer layer of thirteen
trapezoidal
shaped aluminum strands having a diameter of about 1.1080 inches. The total
area of
carbon is about 0.06 in2, of glass is about 0.05in2, of inner aluminum is
about.315 in2
and outer aluminum is about .53 in2. The fiber to resin ratio in the inner
carbon
strength member is 65/35 by weight and the outer glass layer fiber to resin
ratio is
60/40 by weight.
[20] The specifications are summarized in the following table:
[21] E-Glass
Advantex Roving (250Yield)
Tensile Strength, Ksi 770
Elongation at Failure, % 4.5
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Tensile Modulus, Msi 10.5
[22] Carbon (graphite)
[23]
Carbon: Toray T700S (Yield 24K)
Tensile strength, Ksi 711
Tensile Modulus, Msi 33.4
Elongation at Failure, % 2.1%
Density lbs/ft3 0.065
Filament Diameter, in 2.8E-04
[24] Epoxy Matrix System
Araldite MY 721
Epoxy value, equ./kg 8.6-9.1
Epoxy Equivalent, g/equ. 109-
Viscosity @ 50C, cPs 3000-6000
Density @ 25C lb/gal. 1.1501.18
Hardener 99-023
Viscosity @ 25C, cPs 75-300
Density @ 25C, lb/gal 1.19-1.22
Accelerator DY 070
Viscosity @25C, cPs <50
Density @ 25C, lb/gal 0.95-1.05
[25] In an alternate embodiment, S-Glass may be substituted for all or a
portion of the E-
glass in the above example. Values for S-Glass are presented in the table
below.
[26]
S-glass
Tensile Strength, Ksi 700
Elongation at Failure, % 5.6
Tensile Modulus, Msi 12.5
Mode for Invention
[27]
[28] The present invention will now be described more fully hereinafter with
reference
to the accompanying drawings, in which exemplary embodiments of the invention
are
shown. This invention may, however, be embodied in many different forms and
should
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not be construed as limited to the embodiments set forth herein; rather, these
em-
bodiments are provided so that the disclosure will fully convey the scope of
the
invention to those skilled in the art.
[29] An ACCC Reinforced Cable
[30] The present invention relates to a reinforced composite core member,
wherein said
member further comprises an external surface coating. In one embodiment, the
composite core comprises a composite material made from a plurality of fiber
rein-
forcements from one or more fiber types embedded in a matrix. A further
embodiment
of the invention uses the composite core in an aluminum conductor composite
core
reinforced (ACCC) cable. These ACCC cables can provide for electrical power
dis-
tribution wherein electrical power distribution includes distribution and
transmission
cables. FIG. 1 illustrates an embodiment of an ACCC reinforced cable 300. The
embodiment in FIG. 1 illustrates an ACCC reinforced cable comprising a
composite
core 303 further comprising a carbon fiber reinforcement and epoxy resin
composite
inner core 302 and a glass fiber reinforcement and epoxy resin composite outer
core
304, surrounded by a first layer of aluminum conductor 306. The conductor in
this
embodiment comprises a plurality of trapezoidal shaped aluminum strands
helically
surrounding the composite core. The first layer of aluminum is further
surrounded by a
second layer of trapezoidal shaped aluminum conductor 308.
[31] A further embodiment of the invention illustrated in FIG. 1B shows an
ACCC
reinforced cable 300 comprising a composite core 303 further comprising a
carbon
fiber reinforcement and epoxy resin composite inner core 302 and a glass fiber
rein-
forcement and epoxy resin composite outer core 304, surrounded by a protective
coating or film 305. The protective coating will be discussed further below.
The
protective coating is further surrounded by a first layer of conductor 306.
The first
layer is further surrounded by a second layer of conductor 308.
[32] A composite core of the invention can have a tensile strength above 200
Ksi, and
more preferably within the range of about 200 Ksi to about 380 Ksi; a modulus
of
elasticity above 7 Msi, and more preferably within the range of about 7 Msi to
about
37 Msi; an operating temperature capability above -45 C, and more preferably
within
the range of about -45 C to about 240 C or higher; and a coefficient of
thermal
expansion below 1.0 x 10"5 / C, and more preferably within the range of about
1.0 x 10
"5 to about -0.6 x 10"6 / C.
[33] To achieve a composite core in the above stated ranges, different matrix
materials
and fiber types may be used. The matrix and the fiber properties are explained
further
below. First, matrix materials embed the fibers. In other words, the matrix
bundles and
holds the fibers together as a unit - a load member. The matrix assists the
fibers to act
as a single unit to withstand the physical forces on the ACCC cable. The
matrix
material may be any type of inorganic or organic material that can embed and
bundle
the fibers into a composite core. The matrix can include, but is not limited
to, materials
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such as glue, ceramics, metal matrices, resins, epoxies, modified epoxies,
foams,
elastomers, epoxy phenolic blends, or other high performance polymers. One
skilled in
the art will recognize other materials that may be used as matrix materials.
[34] While other materials may be used, an exemplary embodiment of the
invention uses
modified epoxy resins. Throughout the remainder of the invention the term
resin or
epoxy may be used to identify the matrix. However, the use of the terms epoxy
and
resin are not meant to limit the invention to those embodiments, but all other
types of
matrix material are included in the invention. The composite core of the
present
invention may comprise resins having physical properties that are adjustable
to achieve
the objects of the present invention. Further, resins according to the present
invention
comprise a plurality of components that maybe adjusted and modified according
to the
invention.
[35] The present invention may use any suitable resin. In addition, in various
em-
bodiments, resins are designed for ease of fabrication. In accordance with the
invention, various resin viscosities may be optimized for high reactivity and
faster
production line speeds. . In one embodiment, an epoxy anhydride system may be
used.
An important aspect of optimizing the resin system for the desired properties
of the
core as well as fabrication is selecting an optimal catalyst package.
According to the
invention, the catalyst (or'accelerator')should be optimized to generate the
greatest
amount of cure of the resin components in a short time with the least amount
of side
reaction that could cause cracking for instance. In addition, it is further
desirable if the
catalyst is inactive at low temperature for increased pot life and very active
at high
temperatures for the fastest pull times during fabrication.
[36] In one embodiment, a vinyl ester resin may be specifically designed for
high
temperature cure processes. Another example is a liquid epoxy resin that is a
reaction
product of epichlorohydrin and bisphenol-A. Yet another example is a high
purity
bisphenol-A diglycidyl ether. Other examples would include polyetheramides,
bis-
malimides, various anhydrides, or imides. In addition, curing agents may be
chosen
according to the desired properties of the end composite core member and the
processing method. For example, curing agents may be aliphatic polyamines,
polyamides and modified versions of these. Other suitable resins may include
ther-
mosetting resins, thermoplastic resins or thermoplastically modified resins,
toughened
resins, elastomerically modified resins, multifunctional resins, rubber
modified resins,
Cyanate Esters, or Polycyanate resins. Some thermosetting and thermoplastic
resins
may include, but are not limited to, phenolics, epoxies, polyesters, high-
temperature
polymers (polyimides), nylons, fluoropolymers, polyethelenes, vinyl esters,
and the
like. One skilled in the art will recognize other resins that may be used in
the present
invention.
[37] Depending on the intended cable application, suitable resins are selected
as a
function of the desired cable properties to enable the composite core to have
long term
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durability at high temperature operation. Suitable resins may also be selected
according to the process for formation of the composite core to minimize
friction
during processing, to increase processing speed, and to achieve the
appropriate fiber to
resin ratio in the final composite core. In accordance with the invention, the
resins may
comprise a viscosity preferably in the range of about 50 to about 10,000 cPs
and
preferably in the range of about 500 to about 3,000 cPs and more preferably in
the
range of about 800 to about 1800 cPs.
[38] The composite core of the present invention comprises resins having good
mechanical properties and chemical resistance. These resins may be able to
function
with prolonged environmental exposure for at least 40 years of usage. More
preferably,
the composite core of the present invention can comprise resins having good
mechanical properties and chemical, water and UV resistance at prolonged
exposure
for at least about 80 years of usage. Further, the composite core of the
present
invention comprises resins that may operate anywhere from -45 C to 240 C,
or
higher, with minimal reduction of structural performance characteristics at
the
temperature extremes.
[39] According to the present invention, resins may comprise a plurality of
components
in order to optimize the properties of the composite core and the fabrication
process. In
various embodiments, the resin comprises one or more hardener/accelerators to
aid in
the curing process. The accelerators chosen depend on the resin and the die
temperature in the fabrication process. Further, the resin may comprise
surfactants to
aid in reducing surface tension in order to improve production line speeds and
surface
quality. The resin may further comprise clay or other fillers. Such
ingredients add bulk
to the resin and function to reduce costs while maintaining the physical
properties of
the resin. Additional additives may further be added. For example, UV
resistant
additives that make the resins resistant to UV, and coloring additives.
[40] Generally, elongation properties of the resin system should exceed that
of the glass,
carbon, or other fibers being utilized. For example, an embodiment of an epoxy
system
may includea low viscosity multifunctional epoxy resin using an anhydride
hardener
and an imidazol accelerator. An example of this type of epoxy system may be
the
Araldite MY 721/Hardener 99-023/Accelerator DY 070 hot curing epoxy matrix
system by Huntsman Inc. and specified in the like titled data sheet dated
September
2002. The resin has a chemical description of
N,N,N',N'-Tetraglycidyl-4,4'-methylenebisbenzenamine. The hardener is
described as
1H-Imidazole, 1-methyl-1-Methylimidazole. This exemplary resin epoxy system,
modified specifically for the ACCC application can have the following
properties: a
tensile elongation around 3.0% to 5%; a flexural strength around 16.5 Ksi to
19.5 Ksi;
a tensile strength around 6.0 Ksi to 7.0 Ksi; a tensile modulus around 450 Ksi
to 500
Ksi; and a flexural elongation around 4.5% to 6.0%. Another embodiment of an
epoxy
resin system may be a multifunctional epoxy with a cycloaliphatic-amine blend
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hardener. An example of this type of epoxy system may be the JEFFCO
1401-16/4101-17 epoxy system for infusion by JEFFCO Products Inc. and
specified in
the like titled data sheet dated July 2002. This exemplary resin epoxy system
can have
the following properties: a Shore D Hardness around 88D; an ultimate tensile
strength
of 9.7 Ksi; an elongation at tensile strength around 4.5% to 5.0%; an ultimate
elongation around 7.5% to 8.5%; a flexural strength around 15.25 Ksi; and an
ultimate
compressive strength around 14.5 Ksi. These embodiments of the epoxy resin
system
are exemplary and are not meant to limit the invention to these particular
epoxy resin
systems. One skilled in the art will recognize other epoxy systems that will
produce
composite cores within the scope of this invention.
[41] The composite core of the present invention can comprise a resin that is
tough
enough to withstand splicing operations without allowing the composite body to
crack.
The composite core of the present invention may comprise resins having a neat
resin
fracture toughness at least about 0.96 MPa-m'/2.
[42] The composite core of the present invention can comprise a resin having a
low co-
efficient of thermal expansion. A low coefficient of thermal expansion reduces
the
amount of sag in the resulting cable. A resin of the present invention may
have a co-
efficient of thermal expansion below about 4.2 x 10"5 / C and possibly lower
than 1.5 x
10-51 C. The composite core of the present invention can comprise a resin
having an
elongation greater than about 3% or more preferably about 4.5%.
[43] Second, the composite core comprises a plurality of fiber reinforcements
from one
or more fiber types. Fiber types may be selected from: carbon (graphite)
fibers - both
HM and HS (pitch based), Kevlar fibers, basalt fibers, glass fibers, Aramid
fibers,
boron fibers, liquid crystal fibers, high performance polyethylene fibers, or
carbon
nanofibers, steel hardwire filaments, steel wires, steel fibers, high carbon
steel cord
with or without adhesion optimized coatings, or nanotubes. Several types of
carbon,
boron, Kevlar and glass fibers are commercially available. Each fiber type may
have
subtypes that can be variously combined to achieve a composite with certain
charac-
teristics. For instance, carbon fibers may be any type from the Zoltek Panex ,
Zoltek
Pyron , Hexcel, Toray, or Thornel families of products. These carbon fibers
may
come from a PAN Carbon Fiber or a Polyacrylonitrile (PAN) Precursor. Other
carbon
fibers would include, PAN-IM, PAN-HM, PAN-UHM,PITCH, or rayon byproducts,
among others. There are dozens of different types of carbon fibers, and one
skilled in
the art would recognize the numerous carbon fibers that may be used in the
present
invention. There are also numerous different types of glass fibers. For
instance, an A-
Glass, B-Glass, C-Glass, D-Glass, E-Glass, S-Glass, AR-Glass, R -Glass, or
basalt
fibers may be used in the present invention. Fiberglass and paraglass may also
be used.
As with carbon fibers, there are dozens of different types of glass fibers,
and one
skilled in the art would recognize the numerous glass fibers that may be used
in the
present invention. It is noted that these are only examples of fibers that may
meet the
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specified characteristics of the invention, such that the invention is not
limited to these
fibers only. Other fibers meeting the required physical characteristics of the
invention
may be used.
[44] To achieve these physical characteristics, composite cores in accordance
with the
present invention may comprise only one type of fiber. The composite core may
be a
uniform section or layer that is formed from one fiber type and one matrix
type. For
instance, the composite core may be a carbon fiber embedded in resin. The core
may
also be a glass fiber embedded in a polymer, and the core may also be basalt
embedded
in a vinyl ester. However, most cables, within the scope of this invention,
may
comprise at least two distinct fiber types.
[45] The two fiber types may be general fiber types, fiber classes, fiber type
subtypes, or
fiber type genera. For instance, the composite core may be formed using carbon
and
glass. Yet, when an embodiment mentions two or more fiber types, the fiber
types
need not be different classes of fibers, like carbon and glass. Rather, the
two fiber
types may be within one fiber class or fiber family. For instance, the core
may be
formed from E-glass and S-glass, which are two fiber types or fiber subtypes
within
the glass fiber family or fiber class. In another embodiment, the composite
may
comprise two types of carbon fibers. For instance, the composite may be formed
from
IM6 carbon fiber and 1M7 carbon fiber. One skilled in the art will recognize
other em-
bodiments that would use two or more types of fibers.
[46] The combination of two or more fiber types into the composite core member
offers
substantial improvements in strength to weight ratio over conventional
materials, such
as traditional steel non-composites, commonly used for cables in an electrical
power
transmission and distribution system. Combining fiber types also may allow the
composite core to have sufficient stiffness and strength but maintain some
flexibility.
[47] Composite cores of the present invention may comprise fiber tows having
relatively
high yield or small K numbers. A fiber tow is a bundle of continuous
microfibers,
wherein the composition of the tow is indicated by its yield or K number. For
example,
a 12K carbon tow has 12,000 individual microfibers, and a 900 yield glass tow
has 900
yards of length for every one pound of weight. Ideally, microfibers wet out
with resin
such that the resin coats the circumference of each microfiber within the
bundle or
tow. Wetting and infiltration of the fiber tows in composite materials is of
critical
importance to the performance of the resulting composite. Incomplete wetting
results
in flaws or dry spots within the fiber composite that reduce strength,
durability and
longevity of the composite product. Fiber tows may also be selected in
accordance
with the size of fiber tow that the process can handle.
[48] Fiber tows of the present invention for carbon may be selected from 2K
and up, but
more preferably from about 4K to about 50K. Glass fiber tows may be 50 yield
and up,
but more preferably from about 115 yield to about 1200 yield.
[49] For glass fibers, individual fiber size diameters in accordance with the
present
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invention may be below 15 mm, or more preferably within the range of about 8
mm to
about 15 mm, and most preferably about 10 mm in diameter. Carbon fiber
diameters
may be below 10 mm, or more preferably within the range of about 5 mm to about
10
mm, and most preferably about 7 mm. For other types of fibers, a suitable size
range is
determined in accordance with the desired physical properties. The ranges are
selected
based on optimal wet-out characteristics and feasibility of use.
[50] A relative amount of each type of fiber can vary depending on the desired
physical
characteristics of the composite core. For example, fibers having a higher
modulus of
elasticity enable formation of a high strength and high-stiffness composite
core. As an
example, carbon fibers have a modulus of elasticity from 15 Msi and up, but
more
preferably, from about 22 Msi to about 45 Msi; glass fibers are considered low
modulus fibers having a modulus of elasticity of about 6 to about 15 Msi, and
more
preferably in the range of about 9 to about 15 Msi. As one skilled in the art
will
recognize, other fibers may be chosen that can achieve the desired physical
properties
for the composite core. In one example, a composite core may comprise a
substantial
portion of inner advanced composite surrounded by a substantially smaller
outer layer
of low modulus glass fiber. By varying the particular combinations and ratios
of fiber
types, pre-tensioning of the finished core may also be achieved to provide a
compound
improvement in the core's ultimate strength. Carbon Fiber, for instance, which
has a
very low coefficient of thermal expansion and relatively low elongation can be
combined with e-glass (as an example) which has a higher coefficient of
thermal
expansion and greater elongation. By varying the resin chemistry and
processing tem-
peratures, the resulting 'cured' product can be 'tuned' to provide greater
strength than
the sum of the individual strengths of each fiber type. At higher processing
tem-
peratures, the glass fibers expand while the carbon fibers basically don't. In
the
controlled geometry of a processing die, the outcome is that, as the product
exits the
die and begins to cool down to ambient temperature, the glass, in its attempt
to return
to its original length begins to compress the carbon fibers while still
maintaining some
pre tension, based on the ratio of the fiber blend and the resin's physical
characteristics.
The resulting product has a measurably improved tensile and flexural strength
char-
acteristic.
[51] Composite cores of the present invention can comprise fibers having
relatively high
tensile strengths. The degree of initial installed sag in an overhead voltage
power
transmission cable varies as the square of the span length and inversely with
the tensile
strength of the cable. An increase in the tensile strength can effectively
reduce sag in
an ACCC cable. As an example, carbon or graphite fibers may be selected having
a
tensile strength of at least 250 Ksi and more preferably within the range of
about 350
Ksi to about 1000 Ksi, but most preferably, within the range between 710 Ksi
to 750
Ksi. Also as an example, glass fibers can be selected having a tensile
strength at least
about 180 Ksi, and more preferably within the range of about 180 Ksi to about
800
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Ksi. The tensile strength of the composite core can be adjusted by combining
glass
fibers having a lower tensile strength with carbon fibers having a higher
tensile
strength. The properties of both types of fibers may be combined to form a new
cable
having a more desirable set of physical characteristics.
[52] Composite cores of the present invention can have various fiber to resin
volume
fractions. The volume fraction is the area of fiber divided by the total area
of the cross
section. A composite core of the present invention may comprise fibers
embedded in a
resin having at least a 50% volume fraction and preferably at least 60%. The
fiber to
resin ratio affects the physical properties of the composite core member. In
particular,
the tensile strength, flexural strength, and coefficient of thermal expansion
are
functions of the fiber to resin volume. Generally, a higher volume fraction of
fibers in
the composite results in higher performing composite. The weight of the fiber
and
resin matrix will determine the ratio of fiber to resin by weight.
[53] Any layer or section of the composite core may have a different fiber to
resin ratio
by weight relative to the other layers or sections. These differences may be
ac-
complished by selecting and choosing an appropriate number of fibers for the
ap-
propriate resin type to achieve the desired fiber to resin ratio. For example,
a
composite core member having a 3/8' diameter cross-section, consisting of a
carbon
fiber and epoxy layer surrounded by an outer glass and epoxy layer may
comprise 28
spools of 250 yield glass fiber and an epoxy resin having a viscosity of about
1000 cPs
to about 2000 cPs at 50 C. This fiber to resin selection can yield a fiber
to resin ratio
of about 65/45 by weight. Preferably, the resin may be modified to achieve the
desired
viscosity for the forming process. The exemplary composite may also have 28
spools
of 24K carbon fiber and an epoxy resin having a viscosity of about 1000 cPs to
about
2000 cPs at 50 C. This selection can yield a fiber to resin ratio of about
65/35 by
weight. Changing the number of spools of fiber changes the fiber to resin by
weight
ratio, and thereby can change the physical characteristics of the composite
core. Al-
ternatively, the resin may be adjusted to increase or decrease the resin
viscosity to
improve the resin impregnation of the fibers
[54] In various embodiments, the composite core may comprise any one of a
plurality of
geometries. Some of the different embodiments of the various geometries will
be
explained below. In addition, the composite core may further comprise fibers
having
various alignments or orientations. Continuous towing can longitudinally
orient the
fibers along the cable. The core may have a longitudinal axis running along
the length
of the cable. In the art, this longitudinal axis is referred to as the 0
orientation. In most
cores, the longitudinal axis runs along the center of the core. Fibers can be
arranged to
be parallel with this longitudinal axis; this orientation is often referred to
as a 0
orientation or unidirectional orientation. However, other orientations may be
integrated
for various optimization purposes, to address such variables as flexural
strength, for
instance.
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[55] The fibers in the composite core may be arranged in various ways within
the core.
Besides the 0 orientation, the fibers may have other arrangements. Some of
the em-
bodiments may include off-axis geometries. One embodiment of the composite
core
may have the fibers helically wound about the longitudinal axis of the
composite core.
The winding of the fibers may be at any angle from near 0 to near 90 from
the 0
orientation. The winding may be in the + and - direction or in the + or -
direction. In
other words, the fibers may be wound in a clockwise or counterclockwise
direction. In
an exemplary embodiment, the fibers would be helically wound around the lon-
gitudinal axis at an angle to the longitudinal axis. In some embodiments, the
core may
not be formed in radial layers. Rather, the core may have two or more flat
layers that
are compacted together into a core. In this configuration, the fibers may have
other
fiber orientation besides 0 orientation. The fibers may be laid at an angle
to the 00
orientation in any layer. Again, the angle may be any angle + or - from near 0
to near
90 . In some embodiments, one fiber or group of fibers may have one direction
while
another fiber or group of fibers may have a second direction. Thus, the
present
invention includes all multidirectional geometries. One skilled in the art
will recognize
other possible angular orientations.
[56] In various embodiments, the fibers may be interlaced or braided. For
example, one
set of fibers may be helically wound in one direction while a second set of
fibers is
wound in the opposite direction. As the fibers are wound, one set of fibers
may change
position with the other set of fibers. In other words, the fibers would be
woven or
crisscrossed. These sets of helically wound fibers also may not be braided or
interlaced
but may form concentric layers in the core. In another embodiment, a braided
sleeve
may be placed over the core and embedded in the final core configuration.
Also, the
fibers may be twisted upon themselves or in groups of fibers. One skilled in
the art will
recognize other embodiments where the fiber orientation is different. Those
different
embodiments are included within the scope of the invention.
[57] Other geometries are possible beyond the orientation of the fibers. The
composite
core may be formed in different layers and sections. In one embodiment, the
composite
core comprises two or more layers. For example, a first layer may have a first
fiber
type and a first type of matrix. Subsequent layers may comprise different
fiber types
and different matrices than the first layer. The different layers may be
bundled and
compacted into a final composite core. As an example, the composite core may
consist
of a layer made from carbon and epoxy, a glass fiber and epoxy layer, and then
a basalt
fiber and epoxy layer. In another example, the core may comprise four layers;
an inner
layer of basalt, a next layer of carbon, a next layer of glass and an outer
layer of basalt.
All of these different arrangements can produce different physical properties
for the
composite core. One skilled in the art will recognized the numerous other
layer con-
figurations that are possible.
[58] Still another core arrangement may include different sections in the core
instead of
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14
layers. FIG. 2 shows five possible alternate embodiments of the composite
core. These
cross sections demonstrate that the composite core may be arranged in two or
more
sections without those sections being layered. Thus, depending on the physical
charac-
teristics desired, the composite core can have a first section of core with a
certain
composite and one or more other sections with a different composite. These
sections
can each be made from a plurality of fibers from one or more fiber types
embedded in
one or more types of matrices. The different sections may be bundled and
compacted
into a final core configuration.
[59] In various embodiments, the layers or sections may comprise different
fibers or
different matrices. For example, one section of the core may be a carbon fiber
embedded in a thermosetting resin. Another section may be a glass fiber
embedded in
a thermoplastic section. Each of the sections may be uniform in matrix and
fiber type.
However, the sections and layers may also be hybridized. In other words, any
section
or layer may be formed from two or more fiber types. Thus, the section or
layer may
be, as an example, a composite made from glass fiber and carbon fiber embedded
in a
resin. Thus, the composite cores of the present invention can form a composite
core
with only one fiber type and one matrix, a composite core with only one layer
or
section with two or more fiber types and one or more matrices, or a composite
core
formed from two or more layers or sections each with one or more fiber types
and one
or more matrix types. One skilled in the art will recognize the other
possibilities for the
geometry of the composite core.
[60] The physical characteristics of the composite core may also be adjusted
by
adjusting the area percentage of each component within the composite core
member.
For example, by reducing the total area of carbon in the composite core
mentioned
earlier from 0.0634 sq. in. and increasing the area of the glass layer from
0.0469 sq.
in., the composite core member product may reduce stiffness and increase
flexibility.
[61] Advanced composite fibers may be selected from the group having the
following
characteristics: a tensile strength at least about 250 Ksi and preferably in
the range of
about 350 Ksi to about 1000 Ksi; a modulus of elasticity at least 15 Msi and
preferably
within the range of about 22 Msi to about 45 Msi; a coefficient of thermal
expansion at
least within the range of about -0.6 x 10-6 / C to about 1.0 x 10-'/C; a yield
elongation
percent within the range of about 2% to 4%; a dielectric within the range of
about 0.31
W/m=K to about 0.04 W/m-K; and a density within the range of about 0.065
lb/in3 to
about 0.13 lb/in3.
[62] Low modulus fibers may be selected from the group having the following
charac-
teristics: tensile strength within the range about 180 Ksi to 800 Ksi; a
modulus of
elasticity of about 6 to about 15, more preferably about 9 to about 15 Msi; a
coefficient
of thermal expansion within the range of about 5 x 10'6 / C to about 10 x 10"6
/ C; a
yield elongation percent within the range of about 3% to about 6%; a
dielectric within
the range of about 0.034 W/m xK to about 0.04 W/m xK; and a density from 0.060
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lbs/in3 and up, but more preferably from about 0.065 lbs/in3 to about 0.13
lbs/in3.
[63] In one embodiment a composite core may comprise interspersed' high
modulus of
elasticity fibers and low modulus of elasticity fibers. Depending on the
strain to failure
ratio, this type of core may be a single section or layer of hybridized
composite or it
may be formed in several sections of single fiber composite.
[64] In accordance with the present invention, the resins comprising the
composite
matrix can be customized to achieve certain properties for processing and to
achieve
desired physical properties in the end product. As such, the fiber and
customized resin
strain to failure ratio can be determined.
[65] The composite core may also include other surface applications or surface
treatments to the composite core or film around the composite core. Referring
to FIG.
1B for example, a film 305 or coating surrounds the composite core 303. The
film may
include any chemical or material application to the core that protects the
core 303 from
environmental factors, protects the core 303 from wear, or prepares the core
303 for
further processing. Some of these types of treatments may include, but are not
limited
to, gel coats, protective'paintings, or other post or pre-applied finishes, or
films such as
Kapton, Teflon, Tefzel, Tedlar, Mylar, Melbnex, Tednex, PET, PEN, or others.
[66] According to the invention, a protective film provides at least two
effects. First, the
film adheres to the core to protect the core from environmental factors,
thereby po-
tentially increasing longevity. Second, the film lubricates the outside of the
core that is
in contact with the die to ease fabrication and increase processing speeds. In
various
embodiments this material would prevent the often adhesive-like resin matrix
from
contacting the inner surface of the die, thereby enabling dramatically
improved
processing speeds. The effect, essentially, is that the film creates a static
processing en-
vironment within one that is actually dynamic. In various embodiments, the
film may
be a monofilm or a multiple layer film wherein, the multiple layers comprises
multiple
dimensions and / or physical characteristics. For example, the physical
properties of
the inside layer may be compatible in terms of bonding to the core 303, while
the outer
layer(s) may simply be utilized as a non-compatible processing aid.
[67] Some of the material applications may include, but are not limited to,
surface veils
applied to the core, mats applied to the core, or protective or conductive
tapes wrapped
around the core. The tape may include dry or wet tapes. The tapes may include,
but are
not limited to, paper or paper-product tapes, metallic tape (like aluminum
tape),
polymeric tapes, rubber tapes, or the like. Any of these products may protect
the core
from environmental forces like moisture, heat, cold, UV radiation, or
corrosive
elements. Some examples of films may include Kapton, Tefzel (a blend of Teflon
and
Kapton), VB-3, Teflon, PEN and PET (mylar, polyester, etc.). Other
applications and
treatments to the core will be recognized by one skilled in the art and are
included in
the present invention.
[68] Another problem occurs in some steel reinforced or metal reinforced
cables. Steel
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reinforced cables require a measure of sag in the cable between consecutive
towers or
pole structures. The sag in the line allows vibration or sway in the cable,
and, in some
situations, the sag may be subjected to harmonic vibration, Aeolian (wind-
induced)
vibration, or excessive swaying in the cable. At certain wind speeds or due to
envi-
ronmental forces, the cable may vibrate at a harmonic frequency or at such
force that
the cable or the support structures wear or weaken due to stress and strain.
Some envi-
ronmental forces that could cause damaging vibrations may include, but are not
limited
to wind, rain, earthquakes, tidal action, wave action, river flow action,
nearby
automobile traffic, nearby watercraft, or nearby aircraft. One skilled in the
art will
recognize other forces that may cause damaging vibrations. In addition, one
skilled in
the art will recognize that harmonic or damaging vibration is a function of
the material
in the cable, the sag, the length of the span, and the force inducing the
vibration.
[69] One particular problem occurs with cable spans across or near railroad
tracks. The
movement of trains along the railroad tracks and the vibration from powerful
diesel
engines causes vibrations in the railroad tracks and in the ground around the
tracks.
The ground vibrations induce vibrations in electrical poles and support
structures that
hold the electrical cables. The cables in turn vibrate due to the vibrating
support
structures. In some cases, the vibrations in the cables occur at harmonics
that cause
violent or damaging vibration and sway. This harmonic or damaging vibration
causes
stresses in the cable and the support structures. Sag in the ACSR or like
cables
amplifies the effects of the vibrations. In some instances, the sag allows
harmonic
vibrations from the trains. The ACCC cable in proximity to the train tracks is
not
affected by the same vibration effects. Rather, the ACCC cable that runs
parallel or
near the tracks or that crosses over the tracks can have less line sag. The
reduced line
sag or the different properties of the composite core reduce, dampen, or
lessen the
effects of the train caused vibrations.
[70] The present invention helps prevent the harmonic or damaging "sway or
vibration in
electrical cables due to wind or other forces, such as passing trains. First,
the ACCC
cable may be installed differently due to its increased strength to weight
charac-
teristics. The ACCC cable may span distances, with less sag. The ACCC cables
can be
made lighter and stiffer than steel reinforced cables due to the improved
properties of
the inner core explained above. Thus, the problematic frequencies may be
different for
an ACCC cable compared to the steel reinforced cable. The sag amount may be
changed to adjust the frequencies in the cable that can cause damaging
vibration or
sway. The cable sag may be lessened to alter the harmonic or damaging
frequencies
that may be induced in the cable. In addition, cable spans may be changed. Due
to the
increased strength of some ACCC cables, the distance between poles may be
changed
to adjust the damaging frequencies. One skilled in the art will recognize
other in-
stallation possibilities the ACCC cables provide that can help reduce or
eliminate
vibration or sway, especially harmonic or damaging vibration.
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[711 Second, the materials used in the composite core may be adjusted to
dampen
vibrations within the cable. For instance, an elastomer or other material may
be used in
a layer, in a section, or as part of the matrix material of the composite
core. The
presence of the elastomer or other material may function as a dampening
component
that absorbs the vibrations or dissipates the vibrations. In addition, the
fiber types may
be adjusted to dampen vibrations. For instance, a more elastic fiber type,
such as a
polymer fiber, may be used to absorb or dissipate the vibrations. Thus, the
composition
of the composite core may prevent or mitigate vibration forces. One skilled in
the art
will recognize other changes to the composite core that may reduce or
eliminate
vibration or sway, especially harmonic or damaging vibration.
[72] Thirdly, the geometry of the core, as a single or multiple profile can
serve to
provide self-dampening characteristics as its smooth surfaces interact between
themselves and / or the aluminum conductor strands. This interaction 'absorbs'
vibration across a wide array of frequencies and amplitudes which can be
further
adjusted by varying the core component's geometries and / or the installation
tension of
the ACCC cable.
[73] The composite cables made in accordance with the present invention
exhibit
physical properties wherein these certain physical properties may be
controlled by
changing parameters during the composite core forming process. More
specifically, the
composite core forming process is adjustable to achieve desired physical
charac-
teristics in a final ACCC cable.
[74] A Method of Manufacture of a Composite Core for an ACCC reinforced Cable:
[75] Several forming processes to create the composite core may exist, but an
exemplary
process is described hereinafter. This exemplary process is a high-speed
manufacturing
process for composite cores. Many of the processes, including the exemplary
process,
can be used to form the several different composite cores with the several
different
core structures mentioned or described earlier. However, the description that
follows
chooses to describe the high-speed processing in terms of creating a carbon
fiber core
with a glass fiber outer layer, having unidirectional fibers, and a uniformly
layered,
concentric composite core. The invention is not meant to be limited to that
one
embodiment, but encompasses all the modifications needed to use the high-speed
process to form the composite cores mentioned earlier. These modifications
will be
recognized by one skilled in the art.
[76] In accordance with the invention, a multi-phase forming process produces
a
composite core member from substantially continuous lengths of suitable fiber
tows
and heat processible resins. After producing an appropriate core, the
composite core
member can be wrapped with high conductivity material.
[77] A process for making composite cores for ACCC cables according to the
invention
is described as follows. Referring to FIG. 3, the conductor core forming
process of the
present invention is shown and designated generally by reference number 400.
The
CA 02543111 2009-01-14
18
forming process 400 is employed to make continuous lengths of composite core
members
from suitable fiber tows or rovings and resins. The resulting composite core
member
comprises a hybridized concentric core having an inner and outer layer of
uniformly
distributed substantially parallel fibers.
[78] The beginning of the operation will only be described briefly as it is
discussed in
detail in US Pat. No. 7,211,319 and US Pat. No. 7,060,326 and WO 2003/091008.
In starting
the operation, the pulling and winding spool mechanism is activated to
commence pulling. In
one embodiment, unimpregnated initial fiber tows, comprising a plurality of
fibers extending
from the exit end of the process serve as leaders at the beginning of the
operation to pull fiber
tows 402 (and 401) from spools (not shown) through a fiber tow guide and the
composite core
processing system 400. Fiber tows 402, as shown, comprise a center portion of
carbon fibers
401 surrounded by outer fiber tows of glass fiber 402.
[79] Referring to FIG. 3, multiple spools of fiber tows 401 and 402 are
contained within a
dispensing rack system and are threaded through a fiber tow guide (not shown).
The fibers
can be unwound and depending on the desired characteristics of the core, the
fibers may be
kept parallel or the fibers may be twisted during the process. Preferably, a
puller (not shown)
at the end of the apparatus pulls the fibers through the apparatus. Each
dispensing rack can
comprise a device allowing for the adjustment of tension for each spool. For
example, each
rack may have a small brake at the dispensing rack to individually adjust the
tension for each
spool. Tension adjustment minimizes caternary and cross-over of the fiber when
it travels and
aids in the wetting process. In one embodiment, the tows 401/402 may be pulled
through the
guide (not shown) and into a preheating oven that evacuates moisture.
Preferably, the
preheating oven uses continuous circular air flow and a heating element to
keep the
temperature constant. The preheating oven is preferably above 100 C.
[80] The tows 401/402 in one embodiment are pulled into a wet out system. The
wet out
system may be any process or device that can wet the fibers or impregnate the
fibers with
resin. Wet out systems may include incorporating the resin in a solid form
that will be liquefied
during later heating. For instance, a thermoplastic resin may be formed as
several fibers.
These fibers may be interspersed with the carbon and glass fibers of the
exemplary
embodiment. When heat is applied to the bundle of fibers, the thermoplastic
fibers liquefy or
melt and impregnate or wet the carbon and glass fibers.
[81] In another embodiment, the carbon and glass fibers may have a bark or
skin
surrounding the fiber; the bark holds or contains a thermoplastic or other
type resin in a
powder form. When heat is applied to the fibers, the bark melts or evaporates,
the powdered
resin melts, and the melted resin wets the fibers. In another embodiment, the
resin is a film
applied to the fibers and then melted to wet the fibers. In still another
embodiment, the fibers
are already impregnated with a resin-these fibers are known
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in the art as pre-preg tows. If the pre-preg tows are used, no wet out tank or
device is
used. An embodiment of the wet out system is a wet out tank. Hereinafter, a
wet out
tank will be used in the description, but the present invention is not meant
to be limited
to that embodiment. Rather, the wet out system may be any device to wet the
fibers.
The wet out tank is filled with resin to impregnate the fiber tows 401 / 402.
Excess
resin is removed from the fiber tows 401 / 402 during wet out tank exit, and
finally as
the materials are pulled into the initial curing die.
[82] Various alternative techniques well known in the art can be employed to
apply or
impregnate the fibers with resin. Such techniques include for example,
spraying,
dipping, reverse coating, brushing, and resin injection. In an alternate
embodiment,
ultrasonic activation uses vibrations to improve the wetting ability of the
fibers. In
another embodiment, a dip tank may be used to wet out the fibers. A dip tank
has the
fibers drop into a tank filled with resin. When the fibers emerge from the
tank filled
with resin, the fibers are wetted. Still another embodiment may include an
injection die
assembly. In this embodiment, the fibers enter a pressurized tank filled with
resin. The
pressure within the tank helps wet the fibers. The fibers can enter the die
for forming
the composite while still within the pressurized tank. One skilled in the art
will
recognize other types of tanks and wet out systems that may be used.
[83] Generally, any of the various known resin compositions can be used with
the
invention. In an exemplary embodiment, a heat curable thermosetting polymeric
may
be used. The resin may be for example, PEAR (PolyEther Amide Resin), Bis-
maleimide, Polyimide, liquid-crystal polymer (LCP), vinyl ester, high
temperature
epoxy based on liquid crystal technology, or similar resin materials. One
skilled in the
art will recognize other resins that may be used in the present invention.
Resins are
selected based on the process and the physical characteristics desired in the
composite
core.
[84] Further, the viscosity of the resin affects the rate of formation. To
achieve the
desired proportion of fiber to resin for formation of the composite core
member,
preferably, the viscosity range of the resin is within the range of about 50
Centipoise to
about 3000 Centipoise at 20 C. More preferably, the viscosity falls in the
range of
about 800 Centipoise to about 1200 Centipoise at 200 C. A preferred polymer
provides
resistance to a broad spectrum of aggressive chemicals and has very stable
dielectric
and insulating properties. It is further preferable that the polymer meets
ASTIVLE595
outgassing requirements and UL94 flammability tests and is capable of
operating inter-
mittently at temperatures ranging between 180 C and 240 C or higher without
thermally or mechanically damaging the strength of the member.
[85] To achieve the desired fiber to resin wetting ratio, the upstream side of
the wet out
tank can comprise a device to extract excess resin from the fibers. In one
embodiment,
a set of wipers may be placed after the end of the wet out system, preferably
made
from steel chrome plated wiping bars. The wipers can be 'doctor blades' or
other device
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for removing excess resin.
[86] During the wet out process each bundle of fiber contains as much as three
times the
desired resin for the final product. To achieve the right proportion of fiber
and resin in
the cross section of the composite core members, the amount of pure fiber is
calculated. A die or series of dies or wipers are designed to remove excess
resin and
control the fiber to resin ratio by volume. Alternatively, the die and wipers
can be
designed to allow passage of any ratio of fiber to resin by volume. In another
embodiment, the device may be a set of bars or squeeze out bushings that
extract the
resin. These resin extraction devices may also be used with other wet out
systems. In
addition, one skilled in the art will recognize other devices that may be used
to extract
excess resin. Preferably, the excess resin is collected and recycled into the
wet out
tank.
[87] Preferably, a recycle tray extends lengthwise under the wet out tank to
catch
overflow resin. More preferably, the wet out tank has an auxiliary tank with
overflow
capability. Overflow resin is returned to the auxiliary tank by gravity
through the
piping. Alternatively, tank overflow can be captured by an overflow channel
and
returned to the tank by gravity. In a further alternate, the process can use a
drain pump
system to recycle the resin back from the auxiliary tank and into the wet out
tank.
Preferably, a computer system controls the level of resin within the tank.
Sensors
detect low resin levels and activate a pump to pump resin into the tank from
the
auxiliary mixing tank into the processing tank. More preferably, there is a
mixing tank
located within the area of the wet out tank. The resin is mixed in the mixing
tank and
pumped into the resin wet out tank.
[88] Fiber tows 401 /402 are pulled into a die 406 to compact and configure
the tows
401 and 402. One or more dies may be used to compact, to drive air out of the
composite, and to shape the fibers into a composite core. In an exemplary
embodiment,
the composite core is made from two sets of fiber tows - inner segments are
formed
from carbon while outer segments are formed from glass. The first die 406
functions
further to remove excess resin from the fiber resin matrix and may begin
catalyzation
(or'B-Staging') of the resin. The length of the die is a function of the
desired charac-
teristics of the fiber and resin. In accordance with the invention, the length
of the die
406 may range from about 1/2 inch to about 6 feet. Preferably, the die 406
ranges from
about 3inches to 36 inches in length depending on the desired line speed. The
die 406
further comprises a heating element to enable variation of the temperature of
the die
406. For example, in various resin systems it is desirable to have one or more
heating
zones within the die to active various hardeners or accelerators.
[89] The resins used in accordance with the invention may allow the process to
achieve
speeds up to or above 60 ft/min. In one embodiment of the invention, the core
is pulled
from the first die 406 and wrapped with a protective tape, coating or film.
Although
tape, coating and film may be used to describe different embodiments, the term
film is
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used herein to simplify the description and is not meant to be limiting.
[90] In FIG. 3 two large rolls of tape 408 introduce tape into a first carding
plate 410.
The carding plate 410 aligns the tape parallel to each other surrounding the
core. The
core 409 is pulled to a second carding plate 412. The carding plate 412
function is to
progressively fold the tape towards the center core 409. The core 409 is
pulled through
a third carding plate 414. Carding plate 414 functions to fold the tape
towards the
center core 409. Referring again to FIG. 3, the core 409 is pulled through a
fourth
carding plate 416 which functions to further wrap the tape around the core
409.
Although this exemplary embodiment comprises four carding plates, the
invention
may encompass any plurality of plates to encompass the wrapping. The area
between
each die can also be temperature controlled to assist with resin catalyzation
and
processing.
[91] In an alternate embodiment, the tape is replaced by a coating mechanism.
Such
mechanism functions to coat the core 409 with a protective coating. In various
em-
bodiments, the coating may be sprayed on or rolled on by an apparatus adjusted
to
apply the coating from any plurality of angles in relation to the composite
core. For
example, Gelcoat may be applied like a paint using a reverse coating. It is
preferable
that the coating has a fast cure time so it is dry by the time the core and
coating reach
the winding wheel at the end of the process.
[92] Once the core 409 is wrapped with tape, the core 409 is pulled through a
second die
418. The second die 418 functions to further compress and shape the core 409.
The
compaction of all the fiber tows 401 / 402 creates a uniformly distributed,
layered, and
concentric final composite core with the requisite outside diameter. The
second die
also enables the catalyzation process to be completed
[93] Alternatively, the composite core 409 can pulled through a second B-stage
oven to
a next oven processing system wherein the composite core member is cured. The
process determines the curing heat. The curing heat remains constant
throughout the
curing process. In the present invention, the preferred temperature for curing
ranges
from about 350 F to about 500 F. The curing process preferably spans within
the range
of about 3 feet to about 60 feet. More preferably, the curing process spans
within the
range of about 10 feet in length.
[94] After curing, the composite core is pulled through a cooling phase .
Preferably, the
composite core member cools for a distance ranging from about 8 feet to about
15 feet
by air convection before reaching the puller at the end of the process.
Alternatively, the
core may be pulled to a next oven processing system for post curing at
elevated
temperature. The post-curing process promotes increased cross-linking within
the resin
resulting in improved physical characteristics of the composite member. The
process
generally can allow an interval between the heating and cooling process and a
pulling
apparatus at the end of the process to cool the product naturally or by
convection such
that the pulling device used to grip and pull the product will not damage the
product.
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The pulling apparatus pulls the product through the process with precision
controlled
speed.
[95] After the core 409 is pulled through the process, the core may be wound
using a
winding system whereby the fiber core is wrapped around a wheel for storage or
trans-
portation. It is critical to the strength of the core member that the winding
does not
over stress the core by bending. In one embodiment, the core does not have any
twist,
but the fibers are unidirectional. A standard winding wheel has a diameter of
3.0 feet
with the ability to store up to 100,000 feet of core material. The wheel is
designed to
accommodate the stiffness of the composite core member without forcing the
core
member into a configuration that is too tight. The winding wheel must also
meet the
requirements for transportation. Thus, the wheel must be sized to fit under
bridges and
be carried on semi-trailer beds or train beds. In a further embodiment, the
winding
system comprises a means for preventing the wheel from reversing flow from
winding
to unwinding. The means can be any device that prevents the wheel direction
from
reversing for example, a clutch or a brake system.
[96] In a further embodiment, the process includes a quality control system
comprising a
line inspection system. The quality control process assures consistent
product. The
quality control system may include ultrasonic inspection of composite core
members;
record the number of tows in the end product; monitor the quality of the
resin; monitor
the temperature of the ovens and of the product during various phases; measure
formation; or measure speed of the pulling process. For example, each batch of
composite core member has supporting data to keep the process performing
optimally.
Alternatively, the quality control system may also comprise a marking system.
The
marking system may include a system, such as a unique embedded fiber, to mark
the
composite core members with the product information of the particular lot.
Further, the
composite core members may be placed in different classes in accordance with
specific
qualities, for example, Class A, Class B and Class C.
[97] The fibers used to process the composite core members can be interchanged
to meet
specifications required by the final composite core member product. For
example, the
process allows replacement of fibers in a composite core member having a
carbon core
and a glass fiber outer core with high grade carbon and glass. The process
allows the
use of more expensive better performing fibers in place of less expensive
fibers due to
the combination of fibers and the small core size required. In one embodiment,
the
combination of fibers creates a high strength inner core with minimal
conductivity
surrounded by a low modulus nonconductive outer insulating layer. In another
embodiment, the outer insulating layer contributes to the flexibility of the
composite
core member and enables the core member to be wound, stored and transported on
a
transportation wheel. The outer non-ferrous core material will also mitigate
the type of
electrolysis commonly found between a conventional metal core and the
dissimilar
conductor wire (typically an aluminum alloy).
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[98] Changing the composite core design may affect the stiffness and strength
of the
inner core. As an advantage, the core geometry may be designed to achieve
optimal
physical characteristics desired in a final ACCC cable. Another embodiment of
the
invention, allows for redesign of the composite core cross section to
accommodate
varying physical properties and increase the flexibility of the composite core
member.
Referring again to FIG. 2, the different composite shapes change the
flexibility of the
composite core member. The configuration of the fiber type and matrix material
may
also alter the flexibility. The present invention includes composite cores
that can be
wound on a winding wheel. The winding wheel or transportation wheel may be a
com-
mercially available winding wheel or winding drum. These wheels are typically
formed of wood or metal with an inside diameter of 30 to 48 inches.
[99] Stiffer cores may require a larger wheel diameter which are not
commercially
viable. In addition, a larger winding wheel may not meet the transportation
standards
to pass under bridges or fit on semi-trailers. Thus, stiff cores are not
practical. To
increase the flexibility of the composite core, the core may be twisted or
segmented to
achieve a wrapping diameter that is acceptable. In one embodiment, the core
may
include one 360 degree twist of the fiber for every one revolution of core
around the
wheel to prevent cracking. Twisted fiber is included within the scope of this
invention
and includes fibers that are twisted individually or fibers that are twisted
as a group. In
other words, the fibers may be twisted as a roving, bundle, or some portion of
the
fibers. Alternatively, the core can be a combination of twisted and straight
fiber. The
twist may be determined by the wheel diameter limit. The tension and
compaction
stresses on the fibers are balanced by the single twist per revolution.
[100] Winding stress is reduced by producing a segmented core. FIG. 2
illustrates some
examples of embodiments of the core other than the embodiment of the core
shown in
FIG. 1, namely, an inner concentric core surrounded by an outer concentric
core. The
segmented core under the process is formed by curing the section as separate
pieces
wherein the separate pieces are then grouped together. Segmenting the core
enables a
composite member product having a core greater than .375 inches to achieve a
desirable winding diameter without additional stress on the member product.
[101] Variable geometry of the cross sections in the composite core members
may be
processed as a multiple stream. The processing system is designed to
accommodate
formation of each segment in parallel. Preferably, each segment is formed by
exchanging the series of consecutive bushings or dies for bushings or dies
having pre-
determined configurations for each of the passageways. In particular, the size
of the
passageways may be varied to accommodate more or less fiber, the arrangement
of
passageways may be varied in order to allow combining of the fibers in a
different
configuration in the end product and further bushings may be added within the
plurality of consecutive bushings or dies to facilitate formation of the
varied geometric
cross sections in the composite core member. At the end of the processing
system the
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various sections are combined at the end of the process to form the completed
composite cable core that form a unitary (one-piece) body. Alternatively, the
segments
may be twisted to increase flexibility and facilitate winding.
[102] The final composite core can be wrapped in lightweight high conductivity
aluminum forming a composite cable. While aluminum is used in the title of the
invention and in this description, the conductor may be formed from any highly
conductive substance. In particular, the conductor may be any metal or metal
alloy
suitable for electrical cables. While aluminum is most prevalent, copper may
also be
used. It may also be conceivable to use a precious metal, such as silver,
gold, or
platinum, but these metals are very expensive for this type of application. In
an
exemplary embodiment, the composite core cable comprises an inner carbon core
having an outer insulating glass fiber composite layer and two layers of
trapezoidal
formed strands of aluminum.
[103] In one embodiment, the inner layer of aluminum comprises a plurality of
trapezoidal shaped aluminum segments helically wound or wrapped in a counter-
clockwise direction around the composite core member. Each trapezoidal section
is
designed to optimize the amount of aluminum and increase conductivity. The
geometry of the trapezoidal segments allows for each segment to fit tightly
together
around the composite core member.
[104] In a further embodiment, the outer layer of aluminum comprises a
plurality of
trapezoidal shaped aluminum segments helically wound or wrapped in a clockwise
direction around the composite core member. An opposite direction of wrapping
prevents twisting of the final cable. Each trapezoidal aluminum element fits
tightly
with the trapezoidal aluminum elements wrapped around the inner aluminum
layer.
The tight fit optimizes the amount of aluminum and decreases the aluminum
required
for high conductivity.
[105] The final ACCC reinforced cable is created by surrounding the composite
core with
an electrical conductor.
Industrial Applicability
[106] The invention is directed towards electricity transmission cables. The
aluminum
conductor composite core reinforced cables in accordance with the invention
enable an
increase in the load carrying capacity of transmission cables by using
materials having
inherent properties that allow for increased ampacity without inducing
excessive line
sag. Moreover, the cable according to the invention may still use the existing
transmission structures and liens thus facilitating replacement of existing
cable
transmission lines.
